Geology of Somerset


Geology of Somerset

Somerset is a rural county in the southwest of England, covering convert|4171|km2|sqmi|0. It is bounded on the north-west by the Bristol Channel, on the north by Bristol and Gloucestershire, on the north-east by Wiltshire, on the south-east by Dorset, and on the south west and west by Devon. It has broad central plains with several ranges of low hills. The landscape divides into four main geological sections from the Silurian through the Devonian and Carboniferous to the Permian which influence the landscape, together with water-related features.

The low lying areas of the North Somerset Levels and Somerset Levels have been subject to thousands of years of flooding and man's attempts to control the flow of water. In the north of the county the Limestone of the Mendip Hills dominates the landscape, while in the south the Blackdown and Quantock Hills rise out of the levels. The highest areas are on Exmoor. The wide variety of landscapes has led to several areas being designated as Sites of Special Scientific Interest for geological reasons, and support a range of flora and fauna as can be seen from the List of Sites of Special Scientific Interest in Somerset

Rock ages

The oldest rocks are of Silurian age (443–417 million years ago), the most southerly known outcrop of rocks of this age in Britain. They make up a sequence of lavas, tuffs (volcanic ash), shales and mudstones in a narrow outcrop to the northeast of Shepton Mallet, in the eastern Mendip Hills. [cite web|url=http://www.somerset.gov.uk/somerset/media/707F7/Geodiversity%20-%20MOONS%20HILL-REPORT.pdf|title=Moons Hill Quarry, Stoke St Michael, Shepton Mallet|last=Roche|first=David|date=2004|work=Geodiversity Audit of Active Aggregate Quarries|publisher=Somerset County Council|accessdate=2008-08-21] Rocks from the Devonian (417–354 million years ago) are found in much of Exmoor, [cite web|url=http://www.everythingexmoor.org.uk/_G/Geology.php|title=Geology of Exmoor|publisher=Everything Exmoor|accessdate=2008-08-21] the Quantocks and in the cores to the folded masses of the Mendip Hills. Carboniferous Period (354–290 million years ago) rocks are represented by the Carboniferous Limestone that forms the Mendip Hills, rising abruptly out of the flat landscape of the Somerset Levels and Moors. The limestones are very fossiliferous, and contain evidence of the abundant marine life that existed at the at the time of their creation, including fossil crinoids (sea-lilies), corals and brachiopods. At the end of the Permian (290–248 million years ago) and Triassic periods, the Variscan orogeny resulted in the formation of several mountainous areas including Dartmoor in the south, Exmoor and the Quantocks, and the Mendips. In the Taunton area Permian (295–250 million years ago) red sandstones and breccia outcrop, although rocks of Triassic age (248–204 million years ago) underlie much of Somerset and form the solid geology of the Somerset Moors and Levels. [cite web | title=Somerset | work=English Nature, Special Sites, Somerset Geology | url=http://www.english-nature.org.uk/special/geological/sites/area_ID30.asp | accessdate=2006-10-30] There are no glacial deposits.

The Triassic rocks consist of red marls, sandstones, breccias and conglomerates which spread over the older rocks. The Dolometic Conglomerate is an old shingle beach of Keuper Marl age. The Rhaetic Beds are full of fossils due to invasion of the Jurassic Sea. The Lias consists of clays and limestones, the latter being quarried and are famous for their fossils. Blue Lias was used locally both as a building stone and as a source of lime for making Lime mortar. Blue Lias is believed to be quarried on the Polden Hills in the 15th century; and was quarried in Puriton from the early 19th century until the 1973, when the local cement works closed.Dunning, R.W. (1992). "The Victoria History of the Counties of England. A History of the County of Somerset. Volume VI: Andersfield, Cannington< and North Petherton Hundreds (Bridgwater and Neighbouring Parishes)". Oxford: Oxford University Press. ISBN 0-19-722780-5. Page 183.] Above the Lias is the Lower Oolite Series which are chiefly clays and oolile limestone. The famous Bath Stone is obtained from the Great Oolite bed.Hudson, Kenneth (1971). "The Fashionable Stone". Bath: Adams & Dart. ISBN 0-239-00066-8.] Bezzant, Norman (1980). "Out of the Rock...". London: William Heinemann Ltd. ISBN 0-434-06900-0. Page 143.] Oxford Clay is the chief member of the Middle Oolite Series; and above this are the Upper Cretaceous rocks with Gault, Upper Greensand and Chalk. Alluvial flats and peat bogs occupy much of the centre of Somerset.

Coastline

In prehistoric times the coastline of Somerset was very different from the present one, the sea level at the last glacial maximum being some convert|30|m|ft|0 lower than today so that the Bristol Channel was almost non-existent. The Bristol Channel has one of the largest tidal ranges in the world, up to convert|12|m|ft|0 at Burnham-on-Sea for example, [cite web | url= http://www.environment-agency.gov.uk/commondata/acrobat/severnpositionmay2006_1508223.pd | format= PDF | work= UK Environment Agency | title= Severn Estuary Barrage | date= 31 May 2006 | accessdate= 2007-09-03 ] second only to Bay of Fundy in Eastern Canada. [cite book | title= Extreme Depositional Environments: Mega End Members in Geologic Time
first= Marjorie A. last= Chan | coauthors= Archer, Allen William | pages= pp. 151 | location= Boulder, Colorado | isbn= 0813723701 | publisher= Geological Society of America | year= 2003 | url=http://books.google.com/books?id=b3_1Ry0gDqEC&pg=PA152&lpg=PA152&dq=bristol+channel&source=web&ots=TQTXZ-PIhu&sig=SWfR3iDDyDCkMnAjdxboRxBZI2I#PPA151,M1
] [cite web | url= http://www.bbc.co.uk/bristol/content/articles/2005/07/04/bristolchannel_feature.shtml | title= Coast: Bristol Channel | work= BBC | accessdate= 2007-08-27 ] Normal high tide may be enhanced by between convert|3|m|ft|0 and convert|4|m|ft|0 during storm surges.Rippon (1997). "The Severn Estuary: Landscape Evolution and Wetland Reclamation". London: Leicester University Press. ISBN 0-7185-0069-5. Chapter 2: "Creation of the Levels"] This feature has meant that large areas of the county have been liable to flooding by the sea. Thus the present coastline is partly due a belt of marine clay at the coast and partly due to seawalls built to reclaim areas previously flooded at high tide.Williams, Michael (1970). "The Draining of the Somerset Levels". Cambridge: Cambridge University Press. ISBN 0-521-07486-X. Chapter 2: "Draining: The setting of the Somerset Levels".] The coastline contains exposures of Devonian sediments and tectonics west of Minehead adjoining the classic exposures of Mesozoic sediments and structural features which extend eastward to the Parrett estuary cite web | title=Somerset Geology | work=Good rock guide | url=http://mysite.wanadoo-members.co.uk/hughprudden/sgg.htm | accessdate=2006-10-30] forming cliffs along the coastline near Clevedon and near Minehead, [cite web|url=http://www.visitsomerset.co.uk/site/about-somerset/coast|title=Somerset Coast|publisher=Visit Somerset|accessdate=2008-08-20] with low sandhills near Burnham-on-Sea.Rippon (1997). "The Severn Estuary: Landscape Evolution and Wetland Reclamation". London: Leicester University Press. ISBN 0-7185-0069-5. Chapter 1: "Introduction: a regional landscape study".] There are sandy beaches mainly at Burnham-on-Sea, Brean and Weston-super-Mare. [cite web|url=http://www.sedgemoor.gov.uk/index.aspx?articleid=4444|title=Burnham-on-Sea, Berrow and Brean Sands|publisher=Sedgemoor District Council|accessdate=2008-08-20] There are also storm ridges, salt marsh, and sand dunes. [cite journal|last=Kidson|first=Clarence|coauthors=David D. Gilbertson, John R. Haynes, Alan Heywort, Cledwyn E. Hughes Robin C. Whatley |title=Interglacial marine deposits of the Somerset Levels, South West England|journal=Boreas|volume=7|issue=4|pages=215 - 228|url=http://www3.interscience.wiley.com/journal/120060501/abstract?CRETRY=1&SRETRY=0]

Main river valleys

The main valleys between the hills are filled with alluvial deposits from the hills or sea. The county has many small rivers, most of which flow into the Bristol Channel. Many of the latter rivers now have clysts (the local name for a sluice [cite web | title=FOCUS on Industrial Archaeology No. 68, June 2007 | work=Hampshire Industrial Archaeology Society website | url=http://www.hias.hampshire.org.uk/Focus68/focus68.htm | accessdate=2007-10-30] ) on them to control the sea, but formerly they were tidal for some way inland. The main exception to this is the River Parrett, which still has a tidal bore. [cite web|url=http://www.waterscape.com/canals-and-rivers/river-parrett|title=River Parrett|publisher=Waterscape.com|accessdate=2008-08-21] However the Chew and the Frome flow into the Avon which forms most of the northern county boundary with Gloucestershire.Landranger Map 172: Bristol & Bath. Published in 2006 by the Ordnance Survey] The Cale flows into Dorset through the Blackmore Vale, while the Exe flows into Devon. The (Dorset) Axe, the Culm and the Otter rise in Somerset but flow into Dorset.Landranger Map 193: Taunton & Lyme Regis. Published in 2007 by the Ordnance Survey] The courses of the rivers Parrett, Somerset Axe, Brue and Cary run across the Somerset Levels and have generally been changed to improve the flow.Rippon, Stephen (2007). "Waterways and Water Transport on Reclaimed Coastal Marshlands: The Somerset Levels and Beyond". Chapter 8 In: Blair, John (Edr) (2007). "Waterways and Canal-Building in Medieval England". Oxford: Oxford University Press. ISBN 978-0-19-921715-1.] The River Axe rises from Wookey Hole Caves, due to water draining into the ground at swallet holes on top of the Mendips. The river passes through Panborough Moor, Wedmore Moor, Ox Moor, Stoke Moor and Mark Moor and reaches the sea at Uphill (near Weston-super-Mare).Landranger Map 182: Weston-super-Mare. Published in 2005 by the Ordnance Survey]

The River Brue rises at Brewham, close to the county border with Wiltshire. It flows through Bruton and is joined by the rivers Pitt and Alham. The river then flows past East and West Lydford to Baltonsborough and then turns north to Street across Butts Moor, South Moor and Kennard Moor. Originally it then joined the Axe but now it flows west across Westhay Moor, Tealham and Tadham Moors, Chilton Moor, Mark Moor and Huntspill Moor. It is joined by the North Drain and the Hartlake river. In Huntspill Moor the Brue is linked to the man-made Huntspill river by the artificial Cripps river.Williams, Michael (1970). "The Draining of the Somerset Levels". Cambridge: Cambridge University Press. ISBN 0-521-07486-X.] The Brue reaches the sea near Burnham-on-Sea.The River Cary originates in Castle Cary in the east of Somerset. It flows south-west through Cary Moor to Cary Fitzpaine. The river then turns north-west to the north of Somerton. It then used to turn south to join the Parrett but now passes through Somerton Moor and crosses Kings Sedgemoor in an artificial channel, the King's Sedgemoor Drain, joining the Parrett at Dunball north of Bridgwater.

The River Parrett originates at Cheddington, Dorset, just over the border with Somerset. It enters Somerset at Haselbury Plucknett where it is joined by the Broad river. It passes to the east of South Petherton and flows north through Thorney Moor and Muchelney Level and it is then joined by the Isle and (Ivel) Yeo rivers. The Parrett flows through Langport and then through Middle Moor, Aller Moor to Burrowbridge where it is joined by the River Tone. It then passes through Earlake Moor, Hartlake Moor, Weston Level and South Moor. It continues north through Bridgwater, Horsey Level, past Pawlett Ham and Pawlett Level to the coast near Burnham-on-Sea.

The River Tone originates at Beverton Pond on the Brendon Hills in the west of Somerset. It flows south into Clatworthy reservoir and then to GreenhamLandranger Map 181: Minehead & Brendon Hills. Published in 2006 by the Ordnance Survey] where it changes course to go north-east to Taunton. It continues east through West Moor, Curry and Hay Moors and Stan Moor to Burrowbridge where it meets the Parrett.Landranger Map 183: Yeovil & Frome. Published in 2005 by the Ordnance Survey]

The River Exe rises at Exehead on ExmoorLandranger Map 180: Barnstaple & Ilfracombe. Published in 2008 by the Ordnance Survey] and flows south-east to Exton where it is joined by the River Quarme. It then flows south to Exbridge where it meets the Barle and passes into Devon.Landranger Map 192: Exeter & Sidmouth. Published in 2007 by the Ordnance Survey]

Levels and moors

The North Somerset Levels are to the east of Weston-super-Mare, while the Axe valley is separated by the Isle of Wedmore from the Brue valley. The latter is separated by the Polden Hills from the main wetland of the Parrett/Tone/Cary valleys. The Poldens are a low narrow ridge of Blue Lias with alternating bands of limesone and clay. Because of the nature of the Levels and Moors, the Poldens have a significant visual impact.

The Somerset Levels run from the coast up to convert|30|km|mi|0 inland. These wetlands cover convert|600|km2|sqmi|0, most of which is no higher than convert|8|m|ft|0 above sea level.cite book |last=Williams |first=Robin |coauthors=Romey Williams |title=The Somerset Levels |year=1992 |publisher=Ex Libris Press |location=Bradford on Avon |isbn=0948578386 ] There are coastal marine clay deposits, and further inland there are many peaty areas. Dotted within this wetland landscape are slightly raised inter-glacial "islands" called burtles.cite web |url=http://www.english-nature.org.uk/special/geological/sites/area_ID30.asp |title=Somerset |accessdate=2007-06-10 |work=Natural England ] These have been settled from the Mesolithic onward, with wooden causeways linking them to higher ground.cite web |url=http://www.defra.gov.uk/erdp/pdfs/esaspdfs/stage1/SOMHIST.pdf |title=Historical Monitoring in the Somerset Levels and Moors ESA 1987–1994 |accessdate=2007-06-10 |format=PDF |work=DEFRA ] There are also rocky outcrops, such as Brent Knoll and Glastonbury Tor which have also housed ancient settlements.Croft, Robert and Aston, Michael (1993). "Somerset from the air:An Aerial Guide to the Heritage of the County". Taunton: Somerset County Council. ISBN 0-86183-215-9. Chapter 4: "The Somerset Levels and Moors.]

The water levels in the moors and levels are controlled by a series of small narrow canals called rhines (in Avonmouth and Gloucestershire), or rhynes (in Somerset) (both pronounced reens), or reens (in Gwent), along with larger drains, gates and pumping stations. The rhynes are often used as field boundary ditches instead of hedges.Williams, Michael (1970). "The Draining of the Somerset Levels". Cambridge: Cambridge University Press. ISBN 0-521-07486-X. Page 187.] Some parts are allowed to flood in winter. The area is mainly used for grazing but some peat extraction is carried out. [cite web |url=http://www.ramsar.org/features/features_uk_somerset_peatlands.htm |title=Peat Wastage and Wetland Archaeology |accessdate=2007-06-10 |work=The Ramsar Convention on Wetlands ]

Northern uplands

This is the area between the River Avon to the north and the Axe valley. The north of Somerset is dominated by the tableland of the Mendip Hills, an Area of Outstanding Natural Beauty, stretching from Frome in the east to Crook Peak in the west, with outliers of Bleadon Hill and Brean Down as well as Steep Holm in the Bristol Channel. The highest point is Black down at convert|324|m|ft|0. [cite web | title=Mendip Hills An Archaeological Survey of the Area of Outstanding Natural Beauty | work=Somerset County Council Archeological Projects | url=http://www.somerset.gov.uk/media/896B4/MendipAONB.pdf | accessdate=2006-10-28] There is an escarpment facing south to the Levels and Moors while the dip slope to the north is broken up.To the north of Bath are Landsdown, Langridge and Solsbury hills. These are outliers of the Cotswolds. Bath is noted for its thermal waters (48 °C) that are rich in calcium and sodium sulphates. [cite web |url=http://www.romanbaths.co.uk/index.cfm?fuseAction=SM.nav&UUID=F9F320C4-1A95-4C04-AC609094E5B5DFD3 |title=Sacred Spring |accessdate=2007-10-31 |work=Roman Baths Museum Web Site ]

The Old Red Sandstone is a series of red Sandstone, marls and conglomerates. It rises as an anticline in the Mendips and appears in the Avon Gorge and at Portishead. Carboniferous limestone, of maritime origin, covers the sandstone and appears in the Avon Gorge and at Weston-super-Mare where it contains volcanic rocks. [cite book |last=Duff |first=K.L. |authorlink= |coauthors=A.P. McKirdy & M.J. Harley |title=New sites for old: A students guide to the geology of the east Mendips |year=1985 |publisher=Nature Conservancy Council |location= |isbn=0861393198 ] There are outlying hills at Worlebury, Middle Hope, the Failand Ridge, Broadfields Down, Portishead Down and Wrington Hill.

The main geological component of the Mendips is carboniferous limestone and represent the remnants of a much higher range of hills that existed hundreds of millions years ago. [cite web | title=Somerset | work=English Nature, Special Sites, Somerset Geology | url=http://www.english-nature.org.uk/special/geological/sites/area_ID30.asp | accessdate=2006-10-30] This has allowed the formation of features such as Cheddar Gorge, Ebbor Gorge and Burrington Combe.cite book |last=Toulson |first=Shirley |title=The Mendip Hills: A Threatened Landscape |year=1984 |publisher=Victor Gollancz |location=London |isbn=057503453X ] There are a wide variety of Caves of the Mendip Hills and swallett holes caused by dissolution of the rock by water. Further east there are silurian volcanos, Carboniferous limestone outcrops, variscan thrust tectonics, Permo-Triassic conglomerates, sediment-filled fissures, a classic unconformity, Jurassic clays and limestones, Cretaceous Greensand and chalk topped with Tertiary remnants including Sarsen Stones. These sediments have yielded a fairly rich fossil fauna of brachiopods and trilobites indicating that they were deposited in a shallow marine sea into which the lavas were extruded. The rocks are quarried at Moons Hill near Stoke St Michael for aggregate. [cite book |last=Gough |first=J.W. |authorlink= |coauthors= |title=The mines of Mendip |year=1967 |publisher=David & Charles |location=Newton Abbot|id=http://www.amazon.co.uk/o/ASIN/B0000CNKWB ]

Coal measures appear in the Radstock district, and surrounding Somerset coalfield (largely concealed by Triassic and newer rocks). [cite web|url=https://www.og.berr.gov.uk/upstream/licensing/relinqlics/pedl074report.doc|title=PEDL074 Somerset|last=Goodwin|first=Douglas RP|work=Report for GeoMet Operating Inc for Geomet UK Ltd|publisher=Department for Business, Enterprise and Regulatory Reform|accessdate=2008-08-21] There are two series of coal-bearing sandstones and shales separated by Pennant sandstone. Locally the beds are folded and faulted. There were mines in the Radstock and Nailsea areas but these have closed. This was one of the fisrt areas in the world to undergo systematic geological study and mapping by John Strachey and William Smith in the 18th century. [cite web|url=http://www.cartage.org.lb/en/themes/sciences/Earthscience/Geology/AboutGeology/Historyofgeology/Historyofgeology.htm|title=History of Geology|publisher=Cartage.org|accessdate=2008-08-13] [cite web|url=http://www.geolsoc.org.uk/gsl/geoscientist/features/page1017.html|title= Smith's other debt|work=Geoscientist 17.7 July 2007|publisher=The Geological Society|accessdate=2008-08-13] They observed the rock layers, or strata, which led Smith to the creation of a testable hypothesis, which he termed The Principle of Faunal Succession. [As recounted in Simon Winchester, "The Map that Changed the World" (New York: HarperCollins, 2001), pp. 59-91.]

The Mendips were mined for lead, silver, coal, ochre, Fuller's earth and zinc but this has finished.cite book |last=Toulson |first=Shirley |title=The Mendip Hills: A Threatened Landscape |year=1984 |publisher=Victor Gollancz |location=London |isbn=057503453X ] cite book |last=Coysh |first=A.W. |coauthors= E.J. Mason & V. Waite |title=The Mendips |year=1977 |publisher=Robert Hale Ltd |location=London |isbn=0709164262 ] [cite book |last=Gough |first=J.W. |authorlink= |coauthors= |title=The mines of Mendip |year=1967 |publisher=David & Charles |location=Newton Abbot|id=http://www.amazon.co.uk/o/ASIN/B0000CNKWB ] They were also quarried for stone, notably at Bath and Doulting. Today the Mendips are a major source of aggregates. [cite web | title=Mendip Quarry Producers | url=http://www.mendipquarries.co.uk/statistics.html | accessdate=2008-08-21]

outhern uplands

To the south of Somerset there is an upland with a series of rolling valleys and scarps, from Penselwood in the east to the Blackdown Hills, another designated Area of Outstanding Natural Beauty, in the west.cite web|url=http://www.blackdown-hills.net/modules/documents/documents/BlackdownHills%20Plan.pdf|title=Blackdown Hills Plan 2004 – 2009|publisher=Blackdown Hills AONB|format=PDF|accessdate=2008-05-13] This is a geologically complex area of clays, limstone and marl.cite book|last=Hardy|first=Peter|title=The Geology of Somerset|publisher=Ex Libris Press|location=Bradford on Avon|date=1999|isbn=0948578424] The honey-coloured limestone at Ham Hill (also known as Hamdon Hill)is particularly important to geologists because of the assemblages of fossils which it contains, the sedimentary features which it displays and the way it relates to other rocks of equivalent age in the close vicinity. [cite web | title=Ham Hill | url=http://www.english-nature.org.uk/citation/citation_photo/1000144.pdf | accessdate=2006-07-17] It has been quarried since Roman times at least. [cite web|url=http://webapp1.somerset.gov.uk/her/details.asp?prn=55112|title=Roman occupation, Ham Hill, S of Stoke sub Hamdon|work=Somerset Historic Environment Record|publisher=Somerset County Council|accessdate=2008-08-21]

The Blackdowns are on the south-west border of Somerset, extending into Devon. They are composed of Upper Greensand. The scarp faces north and is steep and wooded, with a south facing dip slope. There is an open plateau, which is not as high as the Mendips.

The Quantock Hills are a convert|20|km|mi|0 long broad ridge from the coast near Watchet in the north to near Taunton in the south. They reach convert|384|m|ft|0 high at Wills Neck and are separated from Exmoor and the Brendons by a rift valley. The Quantocks and the Brendon Hills at the eastern end of Exmoor are formed by thick sequences of slates and sandstones of Devonian age that were deposited by large deltas that built out into a shallow sea.cite book |title=Portrait of the Quantocks |last=Waite |first=Vincent |year=1964 |publisher=Robert Hale |location=London |isbn=0709111584 |pages= ]

The Quantock Hills are largely formed by rocks of the Devonian Period, which consist of sediments originally laid down under a shallow sea and slowly compressed into solid rock. In the higher north western areas older Early Devonian rocks, known as Hangman Grits,cite book|last=Dunning|first=Robert|title=Somerset & Avon|publisher=John Bartholomew & Son Ltd|location=Edinburgh|date=1980|pages=123-124|isbn=0702883808] predominate, and can be seen in the exposed rock at West Quantoxhead quarry, which were worked for road building.cite book |title=Portrait of the Quantocks |last=Waite |first=Vincent |authorlink= |coauthors= |year=1964 |publisher=Robert Hale |location=London |isbn=0709111584 |pages= ] Further south there are newer Middle and Late Devonian rocks, known as Ilfracombe beds and Morte Slates. These include sandstone and limestone, which have been quarried near Aisholt. At Great Holwell, south of Aisholt, there is a limestone cave, which is the only one in the Devonian limestone of North Devon and West Somerset. The lower fringes around the hills are composed of younger rocks of the Triassic period, [cite web |url=http://www.somerset.gov.uk/countryside/quantockhills/quantockhillsgeology.htm |title=Quantock Hills Geology |accessdate=2008-03-03 |format= |work=Quantock Hills AONB ] these are known as New Red Sandstone rocks which represent the deposits of large river systems that crossed a desert plain, [cite web | title=Somerset | work=English Nature, Special Sites, Somerset Geology | url=http://www.english-nature.org.uk/special/geological/sites/area_ID30.asp | accessdate=2006-10-30] , and often contain irregular masses or veins of gypsum, which was worked on the foreshore at Watchet. The scarp is to the west with a dip slope to the east. The west side is cut by combes with broad valleys on the east. The hill tops are open heathland with woods on the slopes.

Several areas have outcrops of slates and between St Audries and Kilve, younger rocks of the Jurassic Period can be found. This area falls within the Blue Anchor to Lilstock Site of Special Scientific Interest (SSSI) and is considered to be of international geological importance. [cite web|url=http://www.english-nature.org.uk/citation/citation_photo/1003759.pdf|title=Blue Anchor to Lilstock Coast|work=SSSI citation sheet|publisher=English Nature|accessdate=2008-08-21] At Kilve are the remains of a red brick retort, built in 1924, when it was discovered that the shale found in the cliffs was rich in oil. [cite web | title=Oil retort house | work=Images of England | url=http://www.imagesofengland.org.uk/details/default.aspx?id=265166 | accessdate=2008-08-21] At Blue Anchor the coloured alabaster found in the cliffs gave rise to the name of the colour "Watchet Blue".cite book |title=Curiosities of Somerset |last=Leete-Hodge |first=Lornie |authorlink= |coauthors= |year=1985 |publisher=Bossiney Books |location=Bodmin |isbn=0906456983 |pages=41 ]

Exmoor

Exmoor is a dissected plateau of Devonian sedimentary rock, rising to convert|517|m|ft|0 at Dunkery Beacon. It extends into Devon but the majority of the area is in Somerset. Much of the area is a National Park. [cite web|url=http://www.exmoor-nationalpark.gov.uk/index/learning_about/moor_facts.htm|title=Moor Facts|publisher=Exmoor National Park|accessdate=2008-08-20] The landscape is one of rounded hills, with hogs-back cliffs at the coast due to geological movements. Because of high rainfall there are boggy areas and the part by the Chains is a Geological Conservation Review site recognised as being nationally important for its south-western lowland heath communities and for transitions from ancient semi-natural woodland through upland heath to blanket mire. The Chains provides palynological record of a mid to late Flandrian vegetation history on Exmoor. The pollen sequence in the peat is calibrated by radiocarbon dating.cite web | title=North Exmoor | work=English Nature | url=http://www.english-nature.org.uk/citation/citation_photo/1006541.pdf | accessdate=2006-08-19]

As this area of Britain was not subject to glaciation, the plateau remains as a remarkably old landform. [cite web |url=http://www.exmoor-nationalpark.gov.uk/index/looking_after/looking_after_landscape/geology.htm |title=Geology |accessdate=2007-11-28 |format= |work=Exmoor National Park ] [cite web |url=http://www.english-nature.org.uk/science/natural/NA_HAbDetails.asp?Name=Exmoor+and+the+Quantocks&N=87&H=65 |title=Exmoor and the Quantocks |accessdate=2007-11-28 |format= |work=Natural England ]
Quartz and iron mineralisation can be detected in outcrops and subsoil. The underlying rocks are covered by moors are supported by wet, acid soil.cite web |url=http://www.everythingexmoor.org.uk/_L/Landscape.php |title=Landscape of Exmoor National Park |accessdate=2007-12-03 |format= |work=Everything Exmoor ] The highest point on Exmoor is Dunkery Beacon; at convert|519|m|ft|0 it is also the highest point in Somerset.

Exmoor has convert|55|km|mi|0 of coastline, including the highest cliffs in England, which reach a height of convert|1350|ft|m|0 at Culbone Hill. [cite web |url=http://www.genuki.org.uk/big/eng/SOM/Culbone/index.html |title=Culbone, Somerset |accessdate=2007-10-24 |format= |work=GENUKI ] However, the crest of this coastal ridge of hills is more than convert|1.6|km|mi|1 from the sea. If a cliff is defined as having a slope greater than 60 degrees, the highest cliff on mainland Britain is Great Hangman near Combe Martin at convert|318|m|ft|0 high, with a cliff face of convert|214|m|ft|0.cite web |url=http://www.exmoor-nationalpark.gov.uk/index/learning_about/moor_facts.htm |title=Moor Facts |accessdate=2007-11-28 |format= |work=Exmoor National Park ] Its sister cliff is the convert|218|m|ft|0 Little Hangman, [cite journal|last=Arber|first=Muriel A. |date=Oct. - Dec., 1949|title=Cliff Profiles of Devon and Cornwall|journal=The Geographical Journal|volume=114|issue=4/6|pages=191-197 ] which marks the edge of Exmoor.

Exmoor's woodlands sometimes reach the shoreline, [cite web|url=http://www.exmoor-nationalpark.gov.uk/index/looking_after/looking_after_landscape/woodland_and_trees.htm|title=Woodland and Trees|accessdate=2007-12-08|publisher=Exmoor National Park] especially between Porlock and "The Foreland", where they form the single longest stretch of coastal woodland in England and Wales. [cite web|url=http://www.exmoor-nationalpark.gov.uk/index/looking_after/looking_after_landscape/rivers_coast_lines.htm|title=Landscape / Rivers and the coast|publisher=Exmoor Park|accessdate=2007-12-08] The Exmoor Coastal Heaths have been recognised as a Site of Special Scientific Interest due to the diversity of plant species present. [cite web | title=Exmoor Coastal Heaths | work=English Nature | url=http://www.english-nature.org.uk/citation/citation_photo/1004152.pdf | accessdate=2006-08-12]

The high ground forms the catchment area for numerous rivers and streams. There are about convert|300|mi|km|0 of named rivers on Exmoor. [cite web |url=http://www.exmoor-nationalpark.gov.uk/filex_07.pdf |title=Water on Exmoor - Filex 7 |accessdate=2007-12-03 |format=PDF |work=Exmoor National Park ] The River Exe, from which Exmoor takes its name, [cite web |url=http://www.visit-exmoor.co.uk/site/about-exmoor/countryside |title=Countryside |accessdate=2007-12-07 |format= |work=Vsit Exmoor ] [cite web |url=http://www.equinetourism.co.uk/editorial/exmoorridinginfo.asp |title=Exmoor National Park |accessdate=2007-12-07 |format= |work=Equine Tourism ] rises at Exe Head near the village of Simonsbath, close to the Bristol Channel coast, but flows more or less directly due south, so that most of its length lies in Devon. The river and the Barle Valley are both designated as biological sites of Special Scientific Interest. Another tributary, the River Haddeo, flows from the Wimbleball Lake.

The action of streams has cut combes through the hills down to the sea, which are now wooded, although much of Exmoor is open heathland. There is an outlier of Exmoor at North Hill near Minehead. Iron working was formerly carried out, probably from the Roman period onward. [cite web|url=http://www.somerset.gov.uk/somerset/cultureheritage/heritage/projects/eus/minehead/|title=Minehead|last=Gathercole|first=Clare|work=Somerset Urban Archaeological Survey|publisher=Somerset County Council|accessdate=2008-08-20]

Because Exmoor was a royal forest, ie a hunting reserve, it was unpopulated in Medieval times. The first house on the moor was only built at Simonsbath in 1654. [cite web | title=Simonsbath House Hotel | work=Images of England | url=http://www.imagesofengland.org.uk/details/default.aspx?id=265427 | accessdate=2007-11-27] It was not until the 19th century that farms were built around the moor.

The Brendon Hills are to the east of Exmoor and are an outlier of it. They are separated from Exmoor by the valley of the River Aville. They have the same undulating landscape. The Brendons reach a height of convert|422|m|ft|0 at Lype Hill.cite web|url=http://www.everythingexmoor.org.uk/_B/Brendon_Hills.php|title=Brendon Hills|publisher=Everything Exmoor|accessdate=2008-08-21] Iron ore mining [cite web|url=http://www.english-heritage.org.uk/server/show/nav.001002003004002003002|title=Brendon Hills NMP|work=National Mapping Programme|publisher=English Heritage|accessdate=2008-08-21] was carried out from Roman times up to the early 20th century.

References

ee also

*Somerset
*Geology of the UK
*History of Somerset
*Geology of England

External links

* [http://www.somerset.gov.uk/media/087/B7/Report.pdf The Aggregate Landscape of Somerset: Predicting the Archaeological Resource]


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